John Wheeler

The physicist John Wheeler, who has died aged 96, was a key figure among the international scientists who formed the Manhattan Project and created the first atomic bomb. But he is likely to be better remembered as the man who coined the term "black hole", and that remembrance will be appropriate, because Wheeler was also a talented and committed teacher, and a philosopher of science on a quest for a unified theory of existence, what he called "the perception of how things fit together".

These two strands of Wheeler's career reflected his friendship with the Danish physicist Niels Bohr, which proved crucial to the Manhattan Project. Wheeler's parents were librarians, who moved the family frequently around the US, and encouraged their children's curiosity. Wheeler recalled asking his mother, at the age of four, where the universe ended; his dissatisfaction with her reply led him to science. As a child he developed a fascination with home-made rockets, and once touched an 11,000-volt power line to find out what would happen. Born in Jacksonville, Florida, he went to high school in Baltimore, Maryland, and in 1933, still only 21, he had earned a doctorate in physics from nearby Johns Hopkins University.

He left for Copenhagen to study under Bohr, but not before getting engaged, after only three dates, to Janette Hegner. With Bohr, Wheeler co-wrote the paper which identified U-235 as the isotope of uranium that could be made to fission. But Bohr also opened his eyes to philosophy, inspiring his protege to never fear ideas that might be considered unconventional. As Wheeler's student Richard Feynman, a Nobel prizewinner, said: "Some people think Wheeler's gotten crazy in his later years, but he's always been crazy."

Wheeler returned to America in 1938 as a professor at Princeton, where he could argue physics and philosophy with Albert Einstein. In 1939, Bohr arrived in New York with the news that Nazi scientists had succeeding in splitting the atom. He and Bohr developed a model for fission, and along with Einstein were instrumental in convincing Franklin Roosevelt to commit the immense resources needed to create the atom bomb after America entered the war.

While it was built at Los Alamos, New Mexico, Wheeler supervised the creation of reactors in Hanford, Washington, which produced the necessary plutonium. Meanwhile, his brother Joseph, serving in the army, was killed in Italy, but not before sending Wheeler a note saying "hurry". He never forgot the lives lost before his weapons put an end to the war.

Wheeler returned to Europe on a Guggenheim grant in 1949. But soon after he and Janette settled in Paris, he was asked by Henry Smyth, then head of the Atomic Energy Commission, to return to the US to work on a new weapon. From conversations with Edward Teller, its leading proponent, Wheeler knew this was the hydrogen bomb. He hesitated, but was convinced to join the project at Los Alamos by Bohr's question: "Do you for a moment imagine that Europe would be free of Soviet control today were it not for the atomic bomb?"

The Wheelers never settled in Los Alamos, but his students Ken Ford and John Toll, and his protege Ted Taylor, proved crucial to the development of nuclear fusion. After returning to Princeton, Wheeler was caught up in the political manoeuvring of Teller and his allies. Their target was Robert Oppenheimer, Wheeler's Princeton colleague, and the wartime head of the Manhattan Project at Los Alamos. Now chief of the AEC's general advisory council, and the country's most-respected physicist, Oppenheimer opposed the H-bomb, thinking it unlikely to be successful, and if successful of no tactical use except total destruction.

Working to neutralise Oppenheimer, the head of the congressional atomic energy committee, Brien McMahon, in 1953 commissioned a history of the H-bomb programme, highly critical of Oppenheimer, to be sent to President Eisenhower. Wheeler was asked to check the theoretical material. Notoriously absent-minded, he left six crucial pages on his train to Washington; they were never recovered. Ironically, a year later, Oppenheimer would be deemed a "security risk". Eventually, Teller would become the self-proclaimed "father of the H-bomb", expunging the work of physicists like Stanislaw Ulam from the record.

Wheeler taught at Princeton until retirement at 65 forced a move to the University of Texas, at first grappling with space-time, and coming up with concepts such as "wormholes". He developed a theory, geometrodynamics, attempting to contain physical phenomena in the geometry of curved space-time, but the discovery of exceptions proved it false.

In 1939, Oppenheimer and Harland Snyder had predicted, extrapolating Einstein, the existence of "gravitationally completely collapsed objects", within which the laws of physics would cease to exist. Although Wheeler argued against the concept for years, he eventually came around, and in a talk at the Goddard Institute, New York, in 1967, spontaneously came up with the name "black hole" to describe it.

With his students Kip Thorne and Charles Misner, Wheeler wrote Gravitation (1973), considered the definitive textbook on general relativity. He eventually retired to Hightstown, New Jersey, taking a bus into his office on the nearby Princeton campus, where he wrote his 1998 autobiography Geons, Black Holes and Quantum Foam.

In 2002, he wrote: "How come the universe? How come us? How come anything?" Although Einstein had once asked him whether, if no one looked at it, the moon continued to exist, Wheeler's answer to his "how come?" questions was, "that's us".

In October 2007, Janette died aged 99. They are survived by two daughters and a son.

· John Archibald Wheeler, physicist, born July 9 1911; died April 13 2008